[TargetLowering] Extract simplifySetCCs ctpop into a separate function. NFCI

[craig.topper]

Summary

As requested in D89346 . This allows us to add some early outs.

I reordered some checks a little bit to make the more common bail outs happen earlier. Like checking opcode before checking hasOneUse. And I moved the bit width check to make sure it was safe to look through a truncate to the spot where we look through truncates instead of after.

[spatel]

LGTM

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

EVT ShiftVT = getShiftAmountTy(OpVT, DAG.getDataLayout(),
                                  !DCI.isBeforeLegalize());
   SDValue One = DAG.getConstant(1, DL, ShiftVT);
   SDValue YShl1 = DAG.getNode(ISD::SHL, DL, N1.getValueType(), Y, One);
   if (!DCI.isCalledByLegalizer())
     DCI.AddToWorklist(YShl1.getNode());
   return DAG.getSetCC(DL, VT, X, YShl1, Cond);
 }
 
+static SDValue simplifySetCCWithCTPOP(const TargetLowering &TLI, EVT VT,
+                                      SDValue N0, const APInt &C1,
+                                      ISD::CondCode Cond, const SDLoc &dl,
+                                      SelectionDAG &DAG) {
+  assert(!VT.isVector() && "Vectors are not supported yet!");
+
+  // Look through truncs that don't change the value of a ctpop.
+  SDValue CTPOP = N0;
+  if (N0.getOpcode() == ISD::TRUNCATE && N0.hasOneUse() &&
+      N0.getValueSizeInBits() > Log2_32(N0.getOperand(0).getValueSizeInBits()))
+    CTPOP = N0.getOperand(0);
+
+  if (CTPOP.getOpcode() != ISD::CTPOP || !CTPOP.hasOneUse())
+    return SDValue();
+
+  EVT CTVT = CTPOP.getValueType();
+  SDValue CTOp = CTPOP.getOperand(0);
+
+  // (ctpop x) u< 2 -> (x & x-1) == 0
+  // (ctpop x) u> 1 -> (x & x-1) != 0
+  if ((Cond == ISD::SETULT && C1 == 2) || (Cond == ISD::SETUGT && C1 == 1)) {
+    SDValue NegOne = DAG.getAllOnesConstant(dl, CTVT);
+    SDValue Add = DAG.getNode(ISD::ADD, dl, CTVT, CTOp, NegOne);
+    SDValue And = DAG.getNode(ISD::AND, dl, CTVT, CTOp, Add);
+    ISD::CondCode CC = Cond == ISD::SETULT ? ISD::SETEQ : ISD::SETNE;
+    return DAG.getSetCC(dl, VT, And, DAG.getConstant(0, dl, CTVT), CC);
+  }
+
+  // If ctpop is not supported, expand a power-of-2 comparison based on it.
+  if ((Cond == ISD::SETEQ || Cond == ISD::SETNE) && C1 == 1 &&
+      !TLI.isOperationLegalOrCustom(ISD::CTPOP, CTVT)) {
+    // (ctpop x) == 1 --> (x != 0) && ((x & x-1) == 0)
+    // (ctpop x) != 1 --> (x == 0) || ((x & x-1) != 0)
+    SDValue Zero = DAG.getConstant(0, dl, CTVT);
+    SDValue NegOne = DAG.getAllOnesConstant(dl, CTVT);
+    assert(CTVT.isInteger());
+    ISD::CondCode InvCond = ISD::getSetCCInverse(Cond, CTVT);
+    SDValue Add = DAG.getNode(ISD::ADD, dl, CTVT, CTOp, NegOne);
+    SDValue And = DAG.getNode(ISD::AND, dl, CTVT, CTOp, Add);
+    SDValue LHS = DAG.getSetCC(dl, VT, CTOp, Zero, InvCond);
+    SDValue RHS = DAG.getSetCC(dl, VT, And, Zero, Cond);
+    unsigned LogicOpcode = Cond == ISD::SETEQ ? ISD::AND : ISD::OR;
+    return DAG.getNode(LogicOpcode, dl, VT, LHS, RHS);
+  }
+
+  return SDValue();
+}
+
 /// Try to simplify a setcc built with the specified operands and cc. If it is
 /// unable to simplify it, return a null SDValue.
 SDValue TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
                                       ISD::CondCode Cond, bool foldBooleans,
                                       DAGCombinerInfo &DCI,
                                       const SDLoc &dl) const {
   SelectionDAG &DAG = DCI.DAG;
   const DataLayout &Layout = DAG.getDataLayout();
if (N0.getOpcode() == ISD::SRL && (C1.isNullValue() || C1.isOneValue()) &&
           Cond = ISD::SETEQ;
         }
         SDValue Zero = DAG.getConstant(0, dl, N0.getValueType());
         return DAG.getSetCC(dl, VT, N0.getOperand(0).getOperand(0),
                             Zero, Cond);
       }
     }
 
-    SDValue CTPOP = N0;
-    // Look through truncs that don't change the value of a ctpop.
-    if (N0.hasOneUse() && N0.getOpcode() == ISD::TRUNCATE)
-      CTPOP = N0.getOperand(0);
-
-    if (CTPOP.hasOneUse() && CTPOP.getOpcode() == ISD::CTPOP &&
-        (N0 == CTPOP ||
-         N0.getValueSizeInBits() > Log2_32(CTPOP.getValueSizeInBits()))) {
-      EVT CTVT = CTPOP.getValueType();
-      SDValue CTOp = CTPOP.getOperand(0);
-
-      // (ctpop x) u< 2 -> (x & x-1) == 0
-      // (ctpop x) u> 1 -> (x & x-1) != 0
-      if ((Cond == ISD::SETULT && C1 == 2) || (Cond == ISD::SETUGT && C1 == 1)){
-        SDValue NegOne = DAG.getAllOnesConstant(dl, CTVT);
-        SDValue Add = DAG.getNode(ISD::ADD, dl, CTVT, CTOp, NegOne);
-        SDValue And = DAG.getNode(ISD::AND, dl, CTVT, CTOp, Add);
-        ISD::CondCode CC = Cond == ISD::SETULT ? ISD::SETEQ : ISD::SETNE;
-        return DAG.getSetCC(dl, VT, And, DAG.getConstant(0, dl, CTVT), CC);
-      }
-
-      // If ctpop is not supported, expand a power-of-2 comparison based on it.
-      if (C1 == 1 && !isOperationLegalOrCustom(ISD::CTPOP, CTVT) &&
-          (Cond == ISD::SETEQ || Cond == ISD::SETNE)) {
-        // (ctpop x) == 1 --> (x != 0) && ((x & x-1) == 0)
-        // (ctpop x) != 1 --> (x == 0) || ((x & x-1) != 0)
-        SDValue Zero = DAG.getConstant(0, dl, CTVT);
-        SDValue NegOne = DAG.getAllOnesConstant(dl, CTVT);
-        assert(CTVT.isInteger());
-        ISD::CondCode InvCond = ISD::getSetCCInverse(Cond, CTVT);
-        SDValue Add = DAG.getNode(ISD::ADD, dl, CTVT, CTOp, NegOne);
-        SDValue And = DAG.getNode(ISD::AND, dl, CTVT, CTOp, Add);
-        SDValue LHS = DAG.getSetCC(dl, VT, CTOp, Zero, InvCond);
-        SDValue RHS = DAG.getSetCC(dl, VT, And, Zero, Cond);
-        unsigned LogicOpcode = Cond == ISD::SETEQ ? ISD::AND : ISD::OR;
-        return DAG.getNode(LogicOpcode, dl, VT, LHS, RHS);
-      }
-    }
+    // Optimize some CTPOP cases.
+    if (SDValue V = simplifySetCCWithCTPOP(*this, VT, N0, C1, Cond, dl, DAG))
+      return V;
 
     // (zext x) == C --> x == (trunc C)
     // (sext x) == C --> x == (trunc C)
     if ((Cond == ISD::SETEQ || Cond == ISD::SETNE) &&
         DCI.isBeforeLegalize() && N0->hasOneUse()) {
       unsigned MinBits = N0.getValueSizeInBits();
       SDValue PreExt;
       bool Signed = false;